The present invention relates to silicone foam compositions. More particularly, the present invention relates to a method for reducing the density of silicone foam compositions.
Elastomeric silicone foams are well known in the art. Reference may be made, for example, to U.S. Pat. Nos. 4,189,545; 3,923,705, 4,599,367 and 3,436,366. These foams have excellent physical properties and are useful in a variety of applications, for example, thermal and electrical insulation, flame barriers, and cushions.
However, elastomeric silicone foams have the drawback of being expensive. Thus, although these foams are superior to organic foams in many instances, organic foams are often used instead for economic reasons.
In an effort to overcome the cost disadvantages of silicone foams over organic foams, silicone foam manufacturers are constantly developing techniques for reducing the density of the silicone foam. Methods for reducing the density of silicone foam compositions are disclosed, for example, in U.S. Pat. Nos. 4,418,157, 4,851,452 and 4,879,317.
U.S. Pat. No. 4,879,317 to Smith et al. (Smith), discloses that a substantial reduction in silicone foam density can be achieved by using a hydride polysiloxane in a silicone foamable mixture comprising a vinyl-terminated polydiorganosiloxane, a hydride polysiloxane, a hydroxylated material, and an effective amount of a platinum catalyst, wherein the hydride polysiloxane in such silicone foamable mixture consists essentially of a mixture of a linear hydride polysiloxane and a cyclic hydride polysiloxane. A further reduction is achieved in the Smith foamable composition by using an aqueous mixture of a C.sub.(1-8) alkanol, such as a mixture of water and methanol. It is stated in Smith that densities of less than 20 pounds per cubic feet can be obtained by the method disclosed therein. Densities in the range of 7.5 to 14.1 are reported in the examples to have been obtained.
U.S. Pat. No. 4,418,157 to Modic discloses a method for reducing the density of a silicone foam by mixing a foamable composition containing a polydiorganosiloxane base polymer, an organohydrogen siloxane, and a platinum catalyst, with a resinous copolymer selected from the group consisting of copolymers comprising R.sub.3 SiO.sub.0.5 units and SiO.sub.2 units, and copolymers comprising R.sub.3 SiO.sub.0.5 units, R.sub.2.sup.1 SiO units and SiO.sub.2 units. Densities of 18.7 and 25.7 pounds per cubic foot were obtained in the examples in Modic.
U.S. Pat. No. 4,851,452 to Gross et al. discloses a method for reducing the density of silicone foam by using a platinum catalyst in the form of a mixture of a platinum vinyl siloxane complex and a platinum triaryl phosphine to generate hydrogen in a foamable composition vinyl-terminated polydiorganosiloxane, a hydride polysiloxane, and a hydroxylated material. Densities ranging from 11.2 to 17.5 were obtained in the examples.
It is desirable to provide a method for obtaining silicone foam having reduced density.
It is further desirable to provide a method for obtaining silicone foam having a density of about 5 to about 6.